Various types of electrical devices are subject to damage by electrostatic discharge, including disk drive heads such as giant magnetoresistive (GMR) heads. At least some current GMR disk drive head designs have an electrostatic discharge damage level of as little as 2.4 volts. That is, an electrostatic discharge event of as low as 2.4 volts to one of the inputs of a GMR head may damage the GMR head. Future disk drive head designs may have an even lower electrostatic discharge damage level, such as below 1 volt.
A disk drive head gimbal assembly (HGA) includes a load beam or suspension, a flexure, and a slider that carries or contains the disk drive. The flexure provides an interconnection between the suspension and the slider. One way to cause electrostatic discharge damage to a GMR head on an HGA is to make metal contact to one of the GMR head inputs while the GMR head is electrically floating. “Electrically floating” in this sense means that the GMR head has a resistance to ground that is greater than about 1 e12 Ohms. It is important to note that the GMR head is actually designed to have at least this much resistance to its suspension, so unless the GMR inputs are connected to ground already, it is by design and default “electrically floating.” If the GMR head is electrically floating, then its voltage is in effect uncontrolled.
For devices that are extremely sensitive to electrostatic discharge, like a GMR head, the metal-contact failure voltage of approximately two volts is easily and frequently exceeded. Since an electrically floating GMR head is not tied to ground, a charge on the insulating interconnect, or any other nearby object, can induce a voltage much greater than 10 volts on the GMR head. As such, metal contact to a GMR input may result in a severe electrostatic discharge current transient that may damage the GMR head in less than 1 nanosecond.
The GMR head may be electrically floating until it is connected to a preamplifier. Various tests may be run on the HGA prior to being electrically connected with a preamplifier. The potential for an electrostatic discharge event thereby exists during the running of these tests. Even after the HGA is attached to a single-ended preamp on a head arm or head stack assembly (collectively the HSA), the potential still exists that the GMR head may be damaged by an electrostatic discharge event.